EP0763066B1 - Process for preparing low molecular weight polyacrylic acids with narrow molecular weight distribution in a tubular reactor - Google Patents

Description

Field of the Invention

The invention relates to a process for continuous Production of polyacrylates or polymethacrylates with one Molecular weight up to 9,000 and non-uniformity of less than 1.3, preferably less than 1.0, by homo- or Co-polymerization of water-soluble acrylic compounds in a tubular reactor and the use of these products as Pigment dispersant.

State of the art

The production of low molecular weight polyacrylic acids is known. So in DE-C2 24 61 164 polyacrylic acids with a molecular weight between 300 and 3,000 by polymerization of acrylic acid in an aqueous solution of more than 30% by weight in the presence of per compounds such as e.g. Peroxodisulfate or hydrogen peroxide described. The low molecular weights are due to regulator substances such as thioglycolic acid, mercaptoethanol, butyl mercaptan or also by sulfur-free regulator substances like Obtained isobutyl methyl ketone. Such low molecular weight Polyacrylic acids have the disadvantage that they are because of the regulating substances usually develop strong smells and the end use of low molecular weight polyacrylic acids Lead problems due to the mostly S-containing end groups.

It is also known to have relatively low molecular weight polyacrylic acids by selecting special reaction parameters in the absence of regulators. So in the DE-C2 29 47 622 polyacrylic acids with a molecular weight from 3,000 to 300,000 by continuous polymerization of acrylic acid in the presence of at least 5% by weight Alkyl acrylates described in a 20 to 50% aqueous solution. 2 to 30% by weight of initiators are added, based on the monomers. The preferred starters are redox catalysts, which are usually a mixture of one water-soluble persulfate and a water-soluble Represent bisulfite. Hydroperoxides and Azo compounds can be used as starters. The reaction runs under a pressure of 2.5 to 24.5 bar and one in Reactor measured temperature between 80 and 205 ° C. The Dwell time is 1 to 24 minutes.

The process has the disadvantage that the molecular weight of up to 300,000 for use as a dispersant is high and that due to the adiabatic driving style and the associated high temperature peaks the discoloration of the Polyacrylate is too intense, making it suitable for many applications are not usable, e.g. as a dispersant for inorganic pigments.

In the as yet unpublished German patent application with the file number P 43 04 014.4 the use of a Mixture of hydroperoxide and hydroxylammonium salt as Redox initiator system for the radical polymerization of water-soluble acrylic compounds in the aqueous system Relatively low molecular weight polyacrylates (up to 15,000). According to the teaching of this application The polymers produced are in principle suitable for the Use as dispersants for inorganic pigments with pigment pastes produced by them, however, have a relative high viscosity.

The use of low molecular weight polyacrylic acid as a pigment dispersant is described, for example, in EP-A2 129 329. Polyacrylates which have an average molecular weight (weight average) of up to 6,000 and a polymolecularity index (M _w / M _n ) below 1.5, corresponding to a non-uniformity (M _w / M _n - 1) of 0, are mentioned as particularly suitable , 5, have.
These products are produced via a complex fractionation of prefabricated polymers into a fraction with high and low molecular weight, which requires the use of solvents.

The object of the invention was a method for the production of polyacrylates or To provide polymethacrylates that use of products manufactured by this process as Pigment dispersant for inorganic pigments allowed, without requiring complex fractionation.

Description of the invention

The invention relates to a method for producing of polyacrylates or polymethacrylates with a number average Molecular weight up to 9,000 and non-uniformity of less than 1.3, preferably less than 1.0 continuous polymerization of water-soluble acrylic or methacrylic compounds, in the form of aqueous solutions with 5 up to 60% by weight monomer content, in a tubular reactor with steam feed at the beginning of the reactor, at temperatures of 80 up to 210 ° C, in the absence of regulating the molecular weight Substances in the presence of hydroperoxides and hydroxylammonium salts as a starter.

The monomers to be polymerized are water-soluble acrylic or methacrylic compounds, in particular to acrylic acid and methacrylic acid, their water soluble Salts, especially alkali salts and ammonium salts, and their water soluble esters, acrylamide and water soluble Acrylamides, e.g. 2-Acrylamido-2-methylpropanesulfonic acid Na salt (AMPS) both alone and in a mixture.

Acrylic acid is preferably polymerized alone.

The salts with amines are also included under "ammonium salts" understand. Water-soluble is understood to mean that the monomers at the reaction conditions in the aqueous reaction system are soluble to an extent of 5% by weight.

The term "hydroperoxide" is used to summarize compounds of the general formula R - O - OH, where R symbolizes hydrogen or an alkyl, cycloalkyl or aralkyl group having 1 to 9 carbon atoms. Hydrogen peroxide is preferably used.
The hydroperoxide should be present in a concentration of 0.1 to 5.0, in particular 0.1 to 0.9,% by weight, based on the sum of the monomer solution and the steam fed in.

“Hydroxylammonium salt” means salts of hydroxylamine with the general formula (NH ₂ OH) _n · H _n X, where H _n X symbolizes a mono- or polyvalent acid and n represents the valence from 1 to 3. The preferred acid is sulfuric acid.

The hydroxylammonium salt should be at a concentration of 0.1 to 3.0, in particular from 0.5 to 1.5 wt .-% present be based on the sum of the monomer solution and the feed Steam.

The concentration of the monomers in water is generally 5 to 60% by weight. However, the optimal concentration depends largely from the construction of the continuously working Tube reactor. The preferred monomer concentration is 25 to 50% by weight.

A mixture of the above substances is continuously in polymerized in a suitable reactor. The construction of the reactor the basic sketch can be seen (see Fig. 1). The Monomer solution together with the reducing agent from the Container 1 and with the initiator solution from container 2 brought together what happens with pumps 3 and 4. The Line for the monomer solution is turned on by a heater heated to a maximum of 60 ° C. The static mixer 5 is also tempered. The tubular reactor 6 can be designed as a double-walled tube will.

According to the invention, steam is fed in at the inlet of the tubular reactor together with the metering of the monomers. The steam feed is intended to ensure particularly rapid mixing of the monomer solution with the oxidizing agent and rapid heating of the mixture to the temperature necessary for polymerization.
The steam fed in generally has a steam pressure of 10 to 50 bar, preferably 15 to 42 bar, corresponding to a temperature of 180 to 260 ° C.

The monomer solution is preheated up to 60 ° C. The reaction temperature is in the range of 80 to 210 ° C. Of the Pressure in the tubular reactor should be chosen so that all components stay in the liquid phase. The regulation of Pressure can take place via a needle valve (7). Is preferred a reaction temperature of 120 to 200 ° C in the tubular reactor.

The residence time is generally 2 to 30 minutes, but preferably 5 to 15 minutes.

The usual molecular weight for radical polymerization regulating substances, i.e. compounds with a high Transmission constant, e.g. Mercaptans, halomethanes, Aldehydes or acetals should not be added.

However, not only the immediate reaction products according to the process of the invention are claimed, but also the neutralization products with inorganic or organic bases that can be produced therefrom. Inorganic bases are, for example, the hydroxides of the alkali salts; organic bases are, for example, ammonia and amines.
The neutralization is carried out in particular with alkali metal hydroxide - as a rule with concentrated NaOH at 20 to 25 ° C. - in a nitrogen atmosphere and leads to a pH of 7 to 9, in particular 7.5 to 8.0.

0,15 molare NaCl-Lösung, auf pH = 10,0 mit NaOH eingestellt; Fließrate 1,0 ml/min;

Säulen: Ultra-Hydro-Gel 1x 1000 Angström, 1x 500 Angström, 2x 250 Angström, 2x 120 Angström;

Brechungsindex-Detektor

The process of the invention gives polymers having a number average molecular weight of up to 9,000. The molecular weight is determined by GPC; Polyethylene oxide was used as calibration standards.
The conditions were:

0.15 molar NaCl solution, adjusted to pH = 10.0 with NaOH; Flow rate 1.0 ml / min;

Columns: Ultra-Hydro-Gel 1x 1000 angstroms, 1x 500 angstroms, 2x 250 angstroms, 2x 120 angstroms;

Refractive index detector

The viscosity (according to Brookfield) of a 35% solution in Water is 50 to 200 mPa · s at 25 ° C.

The polymers are characterized by a molecular weight distribution which is determined by the hydroxylammonium salt concentration can be significantly influenced.

In addition, those obtainable by the process according to the invention Polymers largely colorless. The color values are preferably between 5 and 300 after neutralization between 50 and 150, measured according to APHA.

Another advantage of the polymers according to the invention is that that they are largely free of peroxides, so that post-reactions are not to be feared. The peroxide number is very high much less than 10. The peroxide number is determined according to Sully.

Finally, there is also the low content of residual monomers of great importance in the polymers according to the invention. The residual monomer content is max. 5%, preferably Max. 3% and especially less than 1%.

All information on characterization relates to the Polymers after neutralization, if nothing else was said.

The neutralization products according to the invention Process manufactured polyacrylates or polymethacrylates can be used as dispersants for inorganic pigments will.

In a particular embodiment of the invention, the inorganic pigments in aqueous media, e.g. Printing inks and water-based paints, dispersed. Also for making more concentrated The products can be used in aqueous pigment pastes.

Examples of inorganic pigments are talc, heavy spar, the so-called "china clay", e.g. kaolin, iron oxide in its various modifications and chromium oxide. To be favoured Titanium dioxide in its various modifications such as rutile and anatase and calcium carbonate, e.g. used in a precipitated form.

Pigmente in Mengen von 10 bis 90 Gew.%, bevorzugt von 50 bis 80 Gew.%,

Dispergiermittel in Mengen von 0,05 bis 1 Gew.%, bevorzugt von 0,1 bis 0,5 Gew.%

und als Rest Wasser.A typical pigment preparation - based on the preparation in each case - can contain:

Pigments in amounts of 10 to 90% by weight, preferably 50 to 80% by weight,

Dispersant in amounts from 0.05 to 1% by weight, preferably from 0.1 to 0.5% by weight

and the rest water.

It is generally preferred to use as little dispersant as possible to use.

The preparation is generally produced in such a way that the pigments with part of the water and the Dispersant in a suitable aggregate, e.g. one Dissolver, be mixed and then the rest of the water is added with vigorous stirring. Stirring continues continued - usually between 1 and 15 minutes - until the desired degree of dispersion has been reached.

The pigment preparations produced in this way can can be processed immediately, e.g. in the preparation of a water-thinnable lacquer by adding the binder or can also be used as an intermediate, e.g. as Pigment paste in the paint, paper or leather industry.

Examples

Unless otherwise, all percentages are understood noted as a weight percent.

I Structure and mode of operation of the reactor

In the container 1, acrylic acid, the reducing agent and submitted an appropriate amount of water. Via a piston diaphragm pump 3 became the monomer / water / reducing agent mixture promoted in the static mixer. The water / initiator mixture was via a second diaphragm pump 4 also conveyed into the static mixer and with the monomer solution mixed. The monomer template and the piping to the static mixer are with water at 60 ° C preheated. Both the monomer template and the Initiator template and sample templates were made with nitrogen rinsed throughout the test period. The tubular reactor consists of 6 pipes from each 2 m long with an inside diameter of 23.7 mm and a volume of 5.4 l. The reactor tubes are double-walled tubes manufactured. The heating of 3 each pipes connected in series were carried out using thermal oil with electric heating. It became a jacket temperature set from 140 ° C. The print was made with a temperature-resistant needle valve 7 regulated, as a rule a pressure of 10 bar was set. The print was on Output of the reactor measured. Behind the static mixer, on The entrance of the tubular reactor was via an additional line Steam with a steam pressure of 15 to 42 bar and a temperature fed from 180 to 260 ° C.

The samples obtained were in both the acidic and in neutralized form with regard to its viscosity (after Brookfield) at 25 ° C and the color (according to APHA).

The solids content was at 50 ° C and 1 mbar in a vacuum drying cabinet certainly. The molecular weight was determined by GPC (PEG / PEO as standard).

The samples were then mixed with 35% sodium hydroxide solution Neutralized at 25 ° C under nitrogen, up to one pH from 7.5 to 8.0. Of the neutralized products the viscosity and color were determined.

Example 1 is carried out according to the invention with steam feed, a test without steam injection is used for comparison according to P 43 04 014.4.

The reaction parameters are shown in Table 1. Reaction parameters parameter comparison Example 1 Monomer Sol. c _{acrylic acid} 41.4% 65.5% c _HAS 1.06% 1.68% Initiator solution c _H2 O ₂ 2.26% 2.26% Jacket temperature 140 ° C 140 ° C Dwell time 10 min 10 min Dosage Monomer Sol. 27.0 kg / h 17.0 kg / h Initiator solution 5.4 kg / h 5.4 kg / h Steam (23 bar) - 10.0 kg / h Amount of starter, based on acrylic acid + H ₂ O H ₂ O ₂ 0.75% 0.75% HAS 0.9% 0.9% HAS is hydroxylammonium sulfate

The properties of the products neutralized with NaOH are shown in the following table: Properties of the polymers property comparison Example 1 Color according to APHA 81 31 viscosity 250 mPas 60 mPas Solid, in acid 34% by weight 37.5% by weight shape M _n 9,200 6,300 M _w 26,600 10,700 Inconsistency 1.90 0.69

The application properties as dispersants were tested in the following recipe: 63.0 parts Calcium carbonate, Durcal ^(R) 5 7.0 parts TiO ₂ , Kronos ^(R) 2056 0.1 parts Ammonia solution, conc. 29.9 parts Water, fully desalinated 100.0 parts Pigment preparation

To each 100 parts of this pigment preparation, dispersant was added in 0.1% by weight steps in a beaker, based on the active ingredient based on the pigment preparation, mixed for 3 minutes using a dissolver and then the viscosity using the Brookfield viscometer, type LVT, spindle 2, measured.
The lower the viscosity at a certain dispersant concentration, the better the dispersing effect.
The lowest possible concentration of the dispersant is aimed for.

The results are shown in the following table. Efficacy as a dispersant Dispersant Viscosity [mPa · s] after adding 0.1% by weight 0.2% by weight 0.3% by weight example 1 205 125 116 comparison 570 160 125 Hydropalat ^(R) 3043 418 110 108

The results of further Examples 2 to 5 according to the invention are shown in Table 4. Examples according to the invention Example 2 Ex. 3 Ex. 4 Example 5 Monomer solution (kg / h) 17th 13.3 40 40 Initiator solution " 5.4 4.7 14 14 steam " 10th 3.6 10.8 10.8 Pressure of steam (bar) 15 15 23 32 Dwell time (min) 10th 15 5 5 M _n (g / mol) 6350 6000 6250 6510 M _w " 12420 11170 12440 13400 U 0.96 0.86 0.99 1.06 viscosity (mPas) 80 80 120 80 colour APHA 105 50 41 63 Liquefaction effect in mPas after adding 0.1% by weight 215 173 150 200 0.2 " 110 95 100 100 0.3 " 122 105 110 113 0.4 " 126 112 120 120 to a pigment preparation

Claims (7)

1. A process for the production of polyacrylates or polymethacrylates with a number average molecular weight of up to 9,000 and a non-uniformity of less than 1.3 and preferably less than 1.0 by continuous polymerization of water-soluble acrylic or methacrylic compounds in the form of aqueous solutions with a monomer content of 5 to 60% by weight in a tube reactor with introduction of steam at the beginning of the reactor at temperatures of 80 to 210°C, in the absence of molecular weight regulators and in the presence of hydroperoxides and hydroxylammonium salts as initiators.
2. A process for the production of polyacrylates or polymethacrylates by continuous polymerization as claimed in claim 1, characterized in that the water-soluble acrylic or methacrylic compounds used are the acids, preferably acrylic acid.
3. A process for the production of polyacrylates or polymethacrylates by continuous polymerization as claimed in claims 1 and 2, characterized in that the steam is introduced under a pressure of 4 to 50 bar and preferably 15 to 42 bar.
4. A process for the production of polyacrylates or polymethacrylates by continuous polymerization as claimed in claims 1 to 3, characterized in that the polymerization temperature is between 120 and 200°C.
5. A process for the production of polyacrylates or polymethacrylates by continuous polymerization as claimed in claims 1 to 4, characterized in that the hydroperoxide is H₂O₂ and is present in a concentration of 0.1 to 5% by weight and preferably in a concentration of 0.1 to 0.9% by weight, based on the sum of monomer solution and steam.
6. A process for the production of polyacrylates or polymethacrylates by continuous polymerization as claimed in claims 1 to 5, characterized in that the hydroxylamine salt is hydroxylammonium sulfate and is present in a concentration of 0.1 to 3% by weight and preferably in a concentration of 0.5 to 1.5% by weight, based on the sum total of monomer solution and steam.
7. The use of the neutralization products of the polyacrylates or polymethacrylates produced by the process claimed in claims 1 to 6 as dispersants for inorganic pigments.